Prior research shows that adolescent animals are more sensitive to chronic alcohol exposure, with more pronounced alcohol-related memory problems and brain damage than adult animals.

A recent study has found that adolescent rodents are less sensitive to the unpleasant consequences of an alcohol-related hangover, as measured by anxiety.

Such a lack of aversive effects could help establish a persisting cycle of drinking in adolescents, leading to a future of alcohol-related problems.

Many people begin to experiment with alcohol use during adolescence, yet relatively little is known about alcohol’s effects during this critical stage of development. A study in the January issue of Alcoholism: Clinical & Experimental Research uses rodents to assess hangover-related anxiety in both adolescent and adults. Findings indicate that adolescent rodents experience less anxiety during the hangover phase, and recover faster from this hangover effect than do adult rodents, and even show an increase in a specific form of social activity called "play fighting."

"We already know that adolescent rats are more resistant to the motor-impairing, sedative, and social-impairing effects of alcohol than adults," said Elena I. Varlinskaya, associate research professor at Binghamton University and corresponding author for the study. "In contrast, adolescent animals are more sensitive to chronic alcohol exposure, showing more pronounced alcohol-related memory problems and brain damage than adults. Similarly, human adolescents are more vulnerable to the chronic effects of alcohol consumption than adults. They become alcohol dependent in an average of seven months after beginning regular drinking, whereas adults show their first symptoms of alcohol dependency only after three years of regular drinking."

Anxiety, a condition of unsubstantiated feelings of apprehension, is one of the psychological signs of withdrawal from alcohol in alcohol-dependent humans. The more commonly recognized signs of withdrawal are physiological in nature, such as a rapid heartbeat, increased blood pressure, sweating, nausea, and even seizures. Anxiety may also appear in non-dependent individuals following the ingestion of substantial amounts of alcohol; this phenomenon is generally referred to as a "hangover."

"[Scientists have used] the social interaction test in rodents [as] a standard test of anxiety for many years," said Sandra J. Kelly, professor of psychology at the University of South Carolina. In addition, alcohol researchers have used both anti-anxiety and anxiety-provoking drugs in conjunction with alcohol consumption to help establish that increased anxiety leads to the suppression of social interactions that would normally occur when two animals are placed together.

For this study, researchers examined changes in the social interactions of adolescent (110 male, 110 female) and adult (115 male, 115 female) rodents at various times during the recovery period following injection of a single high dose (4 g/kg) of either alcohol or saline.

"As expected, adult animals pre-exposed to alcohol interacted less with their partners than saline-exposed adult animals," said Varlinskaya. "This hangover-associated suppression of social interactions is reminiscent of the suppression in social interactions seen during withdrawal from chronic alcohol. However, adolescent rats not only did not exhibit a hangover-related suppression in social interactions, but they actually showed an increase in an age-specific form of social activity called ‘play fighting.’ Thus, opposite to what is seen in adults, adolescents became more socially responsive during the hangover phase. To our knowledge, this is the first time that such a dramatic age-related difference has been reported in the effects of hangover on social activity."

Both Varlinskaya and Kelly noted that the negative aspects of a hangover can stop people from drinking alcohol, whereas the lack of aversive effects may foster a sense of ‘invulnerability’ and even encourage adolescents to drink.

"We already know that adolescents drink in social situations, in large part to become more relaxed and sociable," said Varlinskaya. "Indeed, animal studies have shown that while under the influence of alcohol, adolescents show greater facilitation of their social interactions than adults. The current results suggest that following a drinking episode, adolescents experience a very unusual hangover effect that is manifested by an increase in social motivation and interactions with peers. This increase in social motivation and desire to interact with peers may provoke adolescents to drink again to gain the social benefits associated with drinking. An alcohol-associated enhancement of social interactions, both during a drinking episode and during the post-alcohol recovery period, could help establish a persisting cycle of drinking in at-risk adolescent individuals which may lead to dependency and a life-long history of alcohol-related problems."

Varlinskaya said future research will again use an animal model to investigate why adolescents and adults manifest alcohol hangovers differently, focusing on brain pathways and systems.

Funding for this Addiction Science Made Easy project is provided by the Addiction Technology Transfer Center National Office, under the cooperative agreement from the Center for Substance Abuse Treatment of SAMHSA.